1. Field of the Invention
The present invention relates to methods of digital processing of signals and to apparatus for performing such methods, and more particularly it relates to methods of recording and reading audio information signals in digital form and to apparatus for performing such methods.
2. Description of the Prior Art
There is known a method of recording and reproducing audio information signals in digital form, according to which a digital signal is directly recorded in a solid-state storage unit. The information thus stored is read out in the very same form in which it has been recorded in the storage (see, for example, DE,A, No. 2826870).
There is also known an apparatus for recording and reading audio information signals in digital form, capable of performing the above method and comprising a series connection of an analog-to-digital (a-d) converter, a solid-state storage unit, a digital-to-analog (d-a) converter, and also an address counter having its outputs connected to the control inputs of the storage unit (see the above-cited Patent).
The above method of recording and reproducing audio information signals in digital form and the above apparatus for performing this method have their capabilities limited by a signal being recorded in a real-time mode, i.e. without compression, so that volumes of processed information are limited.
There is further known a method of recording and reading audio information signals in digital form, including time compression of digital signals with their subsequent recording, and reading the digital signals with their time decompression (see, for Example, U.S. Pat. No. 3860760).
In this method the time compression of digital signals with their subsequent recording is effected by uniform compaction of all the components of a signal in time, thus converting the signal into a different frequency range, which allows storage of substantially greater volumes of data.
In the readout mode, time decompression of digital signals is effected by uniformly extending in time all the signal components, and converting the signal to real-time form.
There is further known an apparatus for recording and reading audio information signals in digital form, capable of performing the last-described method which comprises a series connection of a data input unit, a storage unit and a data output unit, the data input unit having main data inputs and outputs. The control inputs of the data input unit and of the data output unit, respectively, and the timing input of the storage unit have connected thereto the respective outputs of a driver or control unit. The main control inputs of the control unit and the main data outputs of the data output unit are, respectively, the "timing", "recording", "stop" and "repeat" control inputs and the data outputs of the apparatus also have data inputs (see the last-mentioned U.S. Patent).
The last-described method of recording and reading audio information signals in digital form, and the last-described apparatus performing this method have their functioning capabilities extended owing to their ability to compress the digital signals. However, their capabilities are still limited by the fact that all the components of a signal, pauses included, are uniformly subjected to compaction, so that the relative shares of both the useful signals and pauses remain the same in the storage unit notwithstanding the compression.